Homologous and heterologous phosphorylation of the vasopressin V1a receptor

The vasopressin V1a receptor undergoes homologous and heterologous desensit izations which can be mimicked by activation of protein kinase C. This sugg ests that phosphorylation of the V1a receptor may he involved in the desens itization mechanisms. Such a phosphorylation was presently investigated in HEK 293 cells stably transfected with rat vasopressin V1a receptor. Metabol ic labelling and immunoprecipitation of epitope-tagged V1a receptor evidenc ed a 52-kDa band and a 92-kDa band. Glycosidase treatments and immunoblotti ng experiments suggest that the 52-kDa hand corresponds to an immature unpr ocessed receptor protein, whereas the 92-kDa band would correspond to a hig hly glycosylated form of the mature V1a receptor. Exposure of the cells to vasopressin induced a selective P-32 phosphate incorporation in the 92-kDa form of the receptor. This homologous ligand-induced phosphorylation was do se dependent with maximal phosphate incorporation corresponding to four tim es the basal level. Stimulation of the endogenous phospholipase C-coupled m 3 muscarinic receptor by carbachol-induced heterologous phosphorylation of the Via receptor whose amplitude was half that of the homologous phosphoryl ation, This heterologous phosphorylation was associated with a reduced vaso pressin-dependent increase in intracellular calcium. CELL SIGNAL 11;10:743- 751, 1999. (C) 1999 Elsevier Science Inc.